For example, in an NC machine tool, at the time of working a workpiece, a tool such as a drill bit or end mill which is attached to a spindle rotates while contacting the workpiece. The tool is fed in a predetermined feed direction in the NC machine tool. In improvement of the working precision of the workpiece, it is considered necessary to specify the center axis of the tool, which determines the center of rotation of the tool or the posture of the tool, and to set the tool to a desired posture.    PLT 1: Japanese Patent Publication No. 2005-324300A